The present invention relates to the stabilization of a reference d.c. voltage for a semiconductor integrated circuit device having insulated gate field effect transistors.
Recently, reference d.c. voltage generators have been proposed for use in semiconductor integrated circuit (IC) devices to generate stabilized reference d.c. voltages. These voltage generators are normally comprised of semiconductor transistor circuits which are mounted on semiconductive chip substrates of the IC devices. Such on-chip voltage generators receive an external power supply voltage (Vcc) to produce a d.c. voltage. A problem with such devices is that the d.c. potential output level of a reference voltage generator changes with variation or fluctuation in the power supply voltage. If the reference voltage level is changed, a threshold level for determining logic "H" and "L" levels is deviated to thereby degrade the inner logic circuit operations of the semiconductor IC devices.
It is known, in the prior art, that a potential-divider circuit is used as the reference d.c. voltage generator. This circuit is typically formed of a series circuit of insulated gate field effect transistors (FETs) serving as resistive elements. The circuit is supplied, at one terminal, with a d.c. power supply voltage (battery voltage) Vcc to present a given fraction of the voltage Vcc at an output terminal, which is connected to a junction between the FETs. The output d.c. voltage may be supplied to an IC device as the reference voltage. The division of the potential at the output terminal depends upon the magnitudes of the resistances in the potential divider.
In such a circuit configuration, however, accurate stabilization of the reference voltage cannot be expected. This is because the accuracy of stabilization of the reference voltage level should depend upon supplying the potential-divider circuit with a stabilized d.c. power supply voltage. If a potential level of the externally applied voltage fluctuates, it is not possible to obtain an accurate d.c. reference voltage. The result is that the stabilization of reference voltage output level cannot work well.
Further, in the aforementioned voltage generator the voltage-controlling FETs have deviations in their fundamental characteristics due to variations in process parameters, such as gate oxide film thickness, carrier mobility, fabricated size, etc., caused in the manufacturing process thereof. The controlling performance of FETs cannot be set uniform among IC devices in the same manufacturing lots, so that the accuracy of the stabilization of reference voltage output level will be deviated among semiconductor IC devices, which makes it impossible to stabilize a reference voltage in every IC device.